The present invention relates to a fuel consumption indicator for combustion engines.
More particularly, the invention relates to a rate-of-use fuel consumption indicator, i.e. an indicator which provides a vehicle operator with on-going information concerning the rate at which his vehicle uses fuel.
As petroleum-based fuels for combustion engines become increasingly scarce, attempts are being made everywhere to reduce consumption. One such attempt, already required by legislation in certain countries, is to provide devices which will keep the operator of a motor vehicle informed about the fuel-efficiency of his driving behavior, i.e. which will provide him with information concerning the on-going fuel consumption of his combustion engine in order to enable him to vary his driving style so as to obtain greater fuel-efficiency, that is to say lower fuel consumption.
Devices for this purpose are already known and utilize a metering device, for example a turbine flow meter, which meters the fuel passing to the engine. These devices produce a signal, usually an electrical signal, which indicates the amount of fuel flowing to the engine per unit time. This signal is then related in a quotient circuit with a signal which is indicative of the rate of speed of the vehicle and which may be derived from the speedometer, and an outward signal is created which indicates the rate at which fuel is being used per unit distance traveled by the vehicle.
The accuracy of these known devices is not in question; it is adequate in all speed ranges. However, these devices are rather elaborate and therefore expensive and subject to malfunction. In addition, they must necessarily interfere to some extent with the fuel flow and the flow resistance opposed to the fuel by the metering device may, at relatively high ambient temperature, lead to the formation of vapor bubbles in the fuel feeding system, causing what is known as "vapor lock" which stops the engine for lack of fuel passing to it. Even at ordinary ambient temperature, however, there may be considerable interference with the flow of fuel to the engine if, for example, a blockage in the metering device results in a substantial increase in the flow resistance of the fuel.
Another proposal known from the prior art is for a device which senses the pressure in the suction or intake manifold of the engine at a point downstream of the throttle valve, and which indicates this pressure on a measuring device, i.e. a manometer. The indication on the dial of the device is provided either as a "tendency indication" indicating economical and uneconomical driving styles, or it may be provided in terms of an indication of fuel consumption per unit of distance traveled with the vehicle driving in a certain transmission gear, i.e. fourth gear or third gear as a general rule. If an indication of a general tendency is provided, this is usually quite inaccurate; the more specific indication providing information on fuel consumption per unit of distance travelled is only for one particular gear of the transmission and provides no information when the vehicle is driven in one of the other gears. Moreover, the driver has no way of determining from this information which gear would be optimal for the particular operating conditions prevailing at any given time. In fact, incorrect information is even furnished to the driver when he shifts from e.g. fourth gear into third gear, since under these circumstances there is always an indication of a reduction of fuel consumption even though in some circumstances a substantial increase will be the result.
Although it might suggest itself as an obvious remedy to provide the indicating instrument with a second dial which indicates fuel consumption when the vehicle travels in a second one of the gears, e.g. in the third gear, this is actually not feasible in practice because it requires the operator to ascertain, whenever he consults the instrument, in which gear he is driving at this particular time. This is distracting and may cause accidents. Another possibility which is conceivable would be to provide different dials each indicating fuel consumption for a particular gear of the transmission, and an arrangement whereby the dial associated with a particular gear is moved into position for visual observation whenever the operator changes gears. This, however, would be very complicated and, hence, not only expensive but also highly susceptible to malfunctions.